Geopolymer bricks made from less active waste materials

The current study aims at investigating the production feasibility of the geopolymer bricks using the waste materials emanated from the washing process of sand and gravel in aggregate industries. Geopolymer is a material originated by inorganic polycondensation as a result of the alkali activation of aluminosilicate materials. Geopolymer bricks seem to be advantageous due to the low demand for energy and the significant incorporation of wastes. The production of geopolymers from pozzolanic or aluminosilicate rich materials is very common. However, few studies have been carried out on the less-active materials such as waste materials of aggregate industries as raw materials for producing geopolymers. For this purpose, the influence of three parameters, sodium hydroxide concentration (4, 8 and 12 M), calcium hydroxide content (5%,10%, and 15%), and curing temperature (70 degrees C and 105 degrees C), on the physical and mechanical properties of geopolymer bricks was investigated using compressive strength, SEM micrographs, XRD analysis, water absorption, and bulk density. The results indicate that higher sodium hydroxide concentration caused forming a less porous and a more amorphous microstructure, and yielded higher strengths and lower water absorption. The mixtures with higher calcium hydroxide content had higher compressive strengths (up to 75 MPa and 36 MPa at dry and wet conditions, respectively) and a more stable microstructure, however, incorporation of calcium hydroxide at levels higher than 20% results in lower compressive strengths, lower densities, and higher water absorption contents. Increasing curing temperature from 70 degrees C to 105 degrees C increased significantly the compressive strength. (C) 2020 Elsevier Ltd. All rights reserved.